High voltage semiconductor devices sometimes employ field termination structures to block high voltage in a stable and reliable manner. Field termination structures can traditionally be formed from a continuous field plate that is directly coupled to a source terminal of the semiconductor device. During application of a voltage potential between the source and the drain of the semiconductor device the electric potential applied to the source creates an electric field across the field plate to change a state of semiconductor material adjacent the field plate. In some devices the application of an electric field across the field plate blocks the flow of current through the semiconducting material. Because the field plate is a continuous conductor, the electric field may not be uniform across the field plate and may peak at an end of the plate nearest the drain, causing undesirable effects within the semiconductor device. In particular, in some applications the electric field generated by the field plate can be large enough to form hot carriers that are injected into semiconducting or insulating layers that are adjacent the field plate. These hot carriers can then be trapped, and can alter and/or degrade the characteristics of the semiconductor device.
One consequence of these trapped charges can be a reduction in a density of electrons in the two-dimensional electron gas (2DEG) region in the transistor. This reduction may cause a higher on-state resistance that may result in a higher voltage drop during current conduction and higher energy losses. This reduction can be temporary, decaying away in microseconds, or can be longer lasting, such as minutes, hours, or even days. In addition, long-term exposure to high electric fields can increase the leakage of the semiconductor device or even result in physical damage, overheating, or catastrophic failure of the voltage blocking structure and ultimately the entire semiconductor device.
New semiconductor devices can require new features or new methods of forming field termination structures so the electric field is more uniformly distributed across the field termination structure and maintained below the breakdown field of the semiconductor materials while minimizing the space required to support the field such that the reliability, performance and cost of the semiconductor device is optimized.